The present invention relates to material handling generally, and more particularly to a mobile system for loading and unloading railroad cars.
Heretofore various methods for unloading rail cars have been used. One such method involves using a fixed unloading pit that is installed under a rail line. With this method a conveyor is positioned in the pit to transfer the cargo discharged from a rail car to another location, such as a stockpile, for subsequent handling. Among the drawbacks of this system is that it is a fixed site system that limits loading or unloading of rail cars to a particular site, while preferred unloading operations may change to a location along the track far from the fixed pit. These systems also have considerable installation costs due to the substantial amount of excavation required to build the pit beneath the rail line and the construction of support structure to support the rail track above the pit.
Another system for loading and unloading rail cars is disclosed in U.S. Pat. Nos. 4,175,902 and 4,190,394, both to Herzog, et al. This system is comprised of a backhoe that is provided with brackets or special arms for support or engagement with the upper surface of the rail car side walls enabling it to climb on top of a rail car and move from car to car. Although this system is mobile and permits loading and unloading operations to be conducted along a track far from a depot, yard, or other facility where cranes may be used, it is generally limited to unloading rail cars from the top side. Thus, when a backhoe bucket is used with the tractor to unload aggregate from the top of the rail car, a certain amount of material at the bottom of the rail car (which is inaccessible to the bucket due to the bucket configuration) is left behind, thereby decreasing shipping efficiencies. In addition, the material left in the bottom of the rail car generally must be cleaned out prior to reloading the rail car with other material in order to avoid contamination of the subsequently loaded material.
Self-unloading trains also have been constructed in an attempt to improve material handling efficiency. Generally, these trains are a series of two to sixteen rail cars that are interconnected by a conveyor positioned beneath the rail cars. The conveyor leads to one end of the train where a swinging stacker conveyor is located. The swinging conveyor transports the material conveyed beneath the rail cars along the first conveyor to a stockpile, truck, or barge, for example. Although the system can be very effective in delivering large volumes of material by rail, a relatively large length of substantially straight railroad track is required in order that the conveyor belt beneath the rail cars, which transfers material to the swinging stacker conveyor, is sufficiently straight for proper conveyance. In some instances, as much as 1,000 feet of straight track may be required. Another disadvantage of the system is that the cars are custom made for this particular use in such a way that standard bottom-dump rail cars cannot be unloaded with this system. The system's flexibility also is diminished because of the way the bottom side conveyor is integrated with the rail cars. For example, a two car system is not readily converted to a four car system. Thus, when shipping demands double, an additional two car system must be acquired; otherwise, the single two car system must return to the point of origin to reload. The logistics of making two shipments as opposed to one can greatly restrict the system's use. In addition, when hauling different products, such as sand and stone, on one train, contamination of material can result while unloading. This happens when the gate of a rail car having different material than that being conveyed leaks.